* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background: #ececec;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: sans-serif;
}

.calculator {
  background: #1c1c1c;
  border-radius: 30px;
  padding: 20px;
  width: 350px;
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.3);
}

.display {
  background: #333;
  color: white;
  font-size: 2.5rem;
  text-align: right;
  padding: 20px;
  border-radius: 15px;
  margin-bottom: 15px;
  min-height: 60px;
  overflow-x: auto;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.btn {
  font-size: 1.4rem;
  border: none;
  border-radius: 5%;
  padding: 20px;
  cursor: pointer;
  transition: background 0.2s;
}

.btn:active {
  transform: scale(0.95);
}

.gray {
  background: #a5a5a5;
  color: black;
}

.dark {
  background: #333;
  color: white;
}

.orange {
  background: #f1a33c;
  color: white;
}

.zero {
  grid-column: span 2;
  border-radius: 5px;
}

.history {
  background: #222;
  color: #bbb;
  font-size: 1rem;
  text-align: right;
  padding: 8px 15px;
  border-radius: 10px;
  margin-bottom: 5px;
  min-height: 20px;
  overflow-x: auto;
}

body.light {
  background: #f4f4f4;
  color: #222;
}

body.light .calculator {
  background: #fff;
  box-shadow: 0 5px 20px rgba(0, 0, 0, 0.2);
}

body.light .btn.dark {
  background: #e0e0e0;
  color: #000;
}

body.light .btn.orange {
  background: #ff9800;
}

.theme-switch {
  margin-bottom: 15px;
  padding: 8px 12px;
  border-radius: 8px;
  cursor: pointer;
}